Still need another niche to help protect your business from competition, both local and overseas? If your company’s skill set is large, then maybe you should think small, as in very tiny components.
Micro components are not new in the world of manufacturing, but interest in microtechnology is growing. This was evident from the many exhibitors at the PDx/Amerimold trade show in May touting their micromolding capabilities. The evolution of computers, cell phones, and other gadgets, with their need for smaller plastic parts, has opened that world to injection molders and moldmakers.
An LED mold is cut on a Makino ultraprecision vertical machining center.
Micro- and even nano-sized components are taking center stage in manufacturing, but there’s a huge difference between the two. As Mark Kinder, president of Plastic Design Corp. (PDC) in Scottsdale, AZ, noted, “With nano you’re looking at things you can’t see except with a high-powered electron microscope, but micro parts you can see and measure.” Kinder, with Makino’s John Bradford, presented a session on “Machining for Micro Molds” during a seminar at Makino’s technical facility in Mason, OH, opened to customers and potential customers who, like MPW, were in town to attend the PDx/Amerimold trade show.
PDC has four micromolding machines—three Sumitomos and one Fanuc Roboshot—with clamp tonnage of 6, 7, and 18 for implantable medical devices. In addition, PDC uses a 100-ton Roboshot for molding microfluidic test plates. These plates are used in diagnostics laboratory testing, and while the plates are about 3 by 5 inches, each plate has many micro features cut into it (Kinder calls this “micro on macro”) that demand exacting molding performance in PDC’s Class 8 cleanroom. “Any bio burden on the plate itself can really muck up a test,” Kinder said, noting that during the H1N1 virus outbreak a year ago, PDC “went nuts” making enough plates to meet the demand for patient testing.
Forget the data sheet
One downside to molding micro parts is the “mechanical properties go to hell in a handbasket,” said Kinder. “Below 0.020-inch wall section, you lose tensile strength. Heat transfer is a problem, too.”
He explained that because you have so few molecular chains of plastic going into the mold, the plastic behaves differently from when you have a lot of plastic going into the mold. Additionally, when molding micro parts, “You’re slipping the skin and pushing it through the mold. Below ½ mm [500 µm], you can’t keep the core melt going.” As a result of these challenges, PDC always characterizes the plastic before it builds a mold.
If molding is different, so is building a mold for these micro parts. Kinder presented a micro mold construction case history at the Makino seminar. PDC has four Makino machines, two V22s, an Edge 2 Sinker, and a small-wire EDM (U32j) that runs wire in 0.002-, 0.004-, and 0.008-inch diameter.
John Bradford, micromachining R&D manager for Makino, said, “When you get to a feature size below 8 µm, you need ultraprecision machine tools.” The key to machining molds for micromolding, he said, is to control the